FIG. 1 illustrates an example of fall restraint equipment 100 comprising a stairwell 102, a platform 104, handrails 106, and a gangway 108. Stairwell 102 ascends to platform 104, where gangway 108 is connected. An optional cage 110 may be connected to gangway 108 if desired. Handrails 106 are located on the sides of platform 104 that are not connected to either gangway 108 or stairwell 102 in order to prevent a user from proceeding in a direction from the platform that does not lead to the gangway or the stairwell. In this example, the fall restraint equipment provides a user with access to a top 112 of a container 114 (such as a railway car).
FIG. 2 illustrates a gangway 200 that may be used as gangway 108 of FIG. 1. Gangway 200 comprises a base tread 202, which includes two posts or “uprights” 204 connected to base tread support 206. Uprights 204 are typically welded to base tread support 206 but may be connected to the support by other suitable means, such as by bolting. Base tread 202 is conventionally connected to a fixed structure, such as platform 18 (FIG. 1). A support structure or “underbody” 208 is pivotally connected to base tread support 206 at one end and is pivotally connected to another tread 210, such as a seatainer tread, at the other end. Seatainer tread 210 is comprised of uprights 212 and 214 connected to each side of a tread support 216. Each set of uprights 212 and 214 are interconnected by lateral posts 218 and 220. Lateral posts 218 and 220 may be referred to as “joiners,” “connectors,” or “spacer tubes.” In this example, gangway 200 additionally comprises a pair of self-leveling supports 222 pivotally connected to underbody 208. Uprights 212 include top portions 226 that are configured to pivotally receive respective portions of a pair of handrails 224. Likewise, uprights 204 are configured to pivotally receive opposite ends of handrails 224. Gangway 200 may comprise additional components, such as a pair of supports, handrails, or “blocking rails” 228, as desired or needed.
FIG. 3 is a side view of a handrail 300 that may be used as handrail 224 of FIG. 2. Handrail 300 comprises a main body portion 302, a handle portion 304, a pair of end caps 306, a pair of lugs 308, and a pair of bronze bushings 310. Main body portion 302 is a metal tube that is sawed to a specific size from larger metal tubing stock material. As should be understood by those of ordinary skill in the art, the length of main body portion 302 depends on the size of the gangway to which it is attached. Similarly, handle portion 304 is manufactured from a metal tube exhibiting a diameter relatively smaller than that exhibited by the metal tubing used to manufacture main body portion 302. The metal tube is sawed to a specific size from larger stock material and is then bent near both ends at approximately 45° angles. The ends of handle portion 304 are then welded to main body portion 302.
Lugs 308 are also manufactured from larger pieces of stock metal. The stock metal is typically rectangular by nature and must therefore be plasma cut to form lugs 308. Each of lugs 308 is additionally plasma cut in order to define an aperture within the lug. Bronze bushings 310 are then pushed into the aperture, and lugs 308 are welded to main body portion 302. Ends caps 306 are specifically manufactured to fit the distal ends of main body portion 302. After caps 306 have been applied to the ends of main body portion 302, they are welded to the main body portion. Handrail 300 is then powder coated, which also requires heating the handrail. Lugs 308 and bronze bushings 310 are designed to allow handrail 300 to be connected to a gangway. Referring to FIGS. 2 and 3, for instance, the top portions of uprights 204 and 212, such as portions 226, are configured to receive lugs 308. For example, a connecting mechanism such as a carriage bolt or rod is inserted through apertures defined in one side of top portions 226, through bronze bushings 310, and through apertures defined in the other side of the top portions. Handrail 300 is connected to gangway 200 in this manner.
Manufacturing handrail 300 in this manner is both time-consuming and costly. Additionally, the drilling and cutting of the stock materials must be accomplished with precision in order to create a stable end product. Variances greater than an acceptable level render the smaller pieces unusable, which are typically discarded as it is often unfeasible to use them in another product once they have been drilled or cut. Moreover, if other parts cannot be cut or drilled from the remaining portions of the stock materials, they too are discarded. Further, different types and sizes of the metal stock material must be kept on hand in order to form the components of handrail 300 to be welded together. The inefficient yet inescapable use of stock material also increases the costs associated with manufacturing handrail 300.
FIG. 4 illustrates an exemplary rotational molding process for creating a product comprised primarily of plastic. The rotational molding process consists of four separate steps. First, a hollow mold is made of the desired end product. Next, the mold is filled with a predetermined amount of polymer powder or resin. The powder can be pre-compounded to the desired color of the end product. Typically, the powdered resin is polyethylene, polyvinyl chloride (“PVC”), or nylons. An oven is preheated by convection, conduction, radiation, or any other suitable means to a temperature ranging between 500 and 700° F. (260 to 370° C.) depending on the polymer used. Once the powder is loaded into the mold, the mold is closed, locked, and loaded into the oven.
Inside the oven, the mold is rotated about two axes so that the polymer melts and coats the inside of the mold. The rotation speed is relatively slow, such as less than 20 rotations per minute. Those of ordinary skill in the art should understand that the process does not involve centrifugal rotation. Alternatively, the polymer may be melted before rotation of the mold begins. It should be further understood that if the mold is heated for too long a period of time, the polymer will degrade, thereby reducing its impact strength. In contrast, if the mold is heated for too short of a period of time, the polymer will not melt completely and will not fully coalesce on the mold's walls. As a result, large bubbles may be created within the end product. Those of ordinary skill in the art should understand that the amount of time the mold should be heated depends on certain variables including the shape, size, and configuration of the mold, as well as the polymer used. Heat transfer causes the plastic charge inside the mold to melt and uniformly coat or fill the interior of the mold. Additionally, applying a small amount of pressure internally to the mold during the heating process accelerates coalescence of the polymer. As a result, the end product is produced with fewer bubbles and in less time.
Once the heating process is complete, the mold is removed from the oven and cooled, which is typically accomplished though the use of fans. However, water cooling or a combination of the two may be used. Cooling allows the polymer to solidify to the desired shape, as well as shrink slightly so that it may then be handled and removed from the mold. As should be understood, the amount of time required to cool the polymer varies depending on the shape, size, and configuration of the mold, as well as the type of polymer used and the temperature to which it has been heated. It should be further understood that cooling the polymer at a pace too rapid may cause the polymer to shrink too fast and warp the end product.
Once the polymer has cooled sufficiently to be handled so that it can retain the end product's shape, the mold is opened and the product is removed. The process may then be repeated by adding the polymer powder to the mold and repeating.